Automatic and manual power transmissions for vehicles are well-known. Many automatic transmissions include a system of planetary gear sets connected between a torque converter and the output shaft of the transmission. Each planetary gear set includes a sun gear, a ring gear and a plurality of planet gears, supported on a carrier, operatively to connect the sun and ring gears. Various torque transfer devices in the nature of clutches and brakes are utilized in combination with the planetary gear sets to control the rotation of one or more components thereof and thereby produce the desired drive ratios.
Particularly in off-road, and military, vehicle applications, it is desirable to provide multiple reverse drive ratios as well as multiple forward drive ratios. In certain vehicles, one reverse ratio is required, or desired, to be at least equal to fifty percent of the top forward ratio.
Range packs are frequently employed in vehicular transmissions to provide multiple forward and reverse ratios. The range pack often comprises compounded planetary gear sets which provide, for example, four drive gear ratios. An input splitter is typically used in combination with a range pack to permit the same range pack to provide four additional speeds as a result of the gear reducing assemblies within the input splitter.
Most of the range packs currently being used in vehicular transmissions have at least one rotating clutch (usually two) ahead of a series of two or more compounded planetary sets. Selectively applied stationary brakes ground predetermined elements of the planetary gear sets and provide a reaction such that distinct ratios between input and output are generated when a predetermined brake is applied together with a clutch. If there is more than one clutch, the application of both clutches without any brakes being applied normally generates a 1:1 ratio.
The well known reversing set described in U.S. Pat. No. 5,112,285 which is owned by General Motors Corporation, and which is incorporated herein by reference, employs a compound planetary set, a brake, and a clutch. With the carrier as the input, the reversing set may be locked to rotate as a unit when the clutch is applied. When the ring gear of the compound planetary set is grounded, as by a torque transfer device in the nature of a brake, the sun gear of the compound planetary set rotates in a direction opposite to the carrier. As such, the reverse ratio may be approximated by the following mathematical expression: ##EQU1## where, N.sub.s =number of teeth in the sun gear
N.sub.r =number of teeth in the ring gear
If the sun gear has half the number of teeth as that of the reverse assembly ring gear, then the reverse ratio will be 1:-1. If this reversing set is installed in front of a range pack, then an equal number of forward and reverse gears with the same ratios may be generated.